In CDMA cellular communications systems, as CDMA mobile stations move from location to location, neighboring pilot signals are added to and dropped from a candidate set maintained by the mobile station. Particularly, signals are promoted from the neighbor set to the candidate set when the signal satisfies certain criteria. The mobile station communicates candidate set information to the serving base-station for soft hand-off purposes.
In weak signal environments, neighbor signals are sometimes not promoted from the neighbor set to the candidate set fast enough during traffic channel operation to prevent dropping a call, which is undesirable. The delay associated with the promotion of neighbor signals to the candidate set is related to the criteria used to evaluate the suitability of the signals as hand-off candidates. In the Motorola V60c and V60i CDMA cellular handsets neighboring pilot signals assume a pre-candidate status if their signal strength, which is measured as Ec/Io, meets or exceeds an ADD-candidate threshold, TADD. Pilot signals in the pre-candidate set are promoted to the candidate set only if the TADD threshold is maintained over a pre-specified time period, for example, for a predetermined number of scans, thereby preventing the promotion of pilot signals to the candidate set based on spurious signal conditions. When a signal in the candidate set drops below a DROP-threshold, TDROP for a specified time period, the signal is dropped from the candidate set. The DROP-threshold, TDROP, is less than the candidate threshold, TADD.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below.